The present invention relates to a method and a circuit which allow to automatically obtain a forward or a reversed biased photodiode detection device. The invention may for example be used in optical disk players and/or recorders.
In many applications where light is used e.g. as a tool to work on material or as a means to scan information stored on an information medium, thus applications in which a light source is involved, it appears necessary to keep a light intensity constant at a predetermined level at some stage of a process. Typically the light intensity is measured using a photodetector, a result of this measurement is compared with a reference value and a power fed to the light source accordingly regulated.
For some applications it is common to use photodiodes to measure the light intensity, these being a kind of photodetector which in practice may be used in a photodiode circuit of a forward biased or a reversed biased type. The use of either a forward biased or a reversed biased photodiode circuit is typically subjected to an availability of either one type of photodiode circuit on the market. For reasons of flexibility to market conditions a light intensity measuring circuit using photodiodes should be able to use either one of the forward biased or reversed biased photodiode circuit.
A configuration known from prior art and shown in FIG. 1 is used to regulate a light intensity emitted by a light source 1. Either one of a reversed biased photodiode circuit 2 or a forward biased photodiode circuit 3 may be used to determine a light intensity emitted by the light source 1. Either one of photodiode circuits 2 or 3 is connected to an input 4 of a detection device 5 (shown by a dotted connection line). The detection device comprises switches 6 and 7 which may simultaneously be switched when an appropriate signal is applied to a switching control input 8. In case the forward biased photodiode circuit 3 is connected to the input 4 the switches 6 and 7 are switched to the state H and a photovoltage at input 4 is directly transmitted to power regulating means 9. The power regulating means 9 allow to compare the photovoltage to a reference photovoltage and accordingly regulate a power amplitude fed to the light source I in order to maintain a value of the photovoltage to a value of the referenced photovoltage. In an alternative case where the reversed biased photodiode circuit 2 is connected to the input 4 the switches 6 and 7 are switched to the position L. A photovoltage at the input 4 is inverted by the inverter 10 before being transmitted to the power regulating means 9.
A drawback of the known configuration in FIG. 1 is that when either photodiode circuit 2 or 3 is connected to the input 4 the appropriate signal has to be applied to the switching control input 8 by means of an external intervention on the switching control input 8 e.g. by soldering (or de-soldering) the switching control input 8 to (from) ground. The known configuration is typically realized as part of an integrated circuit and the switching control input 8 is one of many pins of this integrated circuit. Soldering the single switching control input pin of the integrated circuit to ground is a delicate manufacturing process which is subject to errors.
It is an object of the invention to find a solution for a detection method or circuit in which either one of a forward biased or a reversed biased photodiode circuit may be used but in which the need for an external intervention on the detection circuit to adapt the detection circuit to the type of photodiode circuit connected to it is eliminated.
A solution to the above described problem is according to the present invention found in a method for automatically identifying a first or a second type of photodiode circuit which each have a first and a second output (or xe2x80x9coutput terminalxe2x80x9d) and which comprises the steps of:
connecting the first output to ground,
connecting to the second output a current source of a predetermined current value,
comparing a voltage at the second output with a predetermined reference voltage,
emitting a signal indicating a result of the comparing which allows an identification of either the first or the second type of photodiode circuit.
The steps of the method according to the invention may be performed automatically and identify a first or a second type of photodiode circuit, e.g. a forward biased or a reversed biased photodiode type circuit.
Another solution to the above described problem is according to the invention found in a method for automatically obtaining a forward or a reversed biased photodiode device which delivers between a first and a second electrode a photovoltage of a predetermined polarity, depending on either one of a first or a second type of photodiode circuit which each have a first and a second output. The method comprises the steps of:
connecting the first output to ground,
connecting to the second output a current source of a predetermined current value,
comparing a voltage at the second output with a predetermined reference voltage,
emitting a signal indicating a result of the comparing which allows an identification of at least the second type of photodiode circuit,
storing the signal,
disconnecting the first output from ground and the second output from the current source,
connecting the first and the second output to the first and second electrode respectively,
maintaining the second output at a constant reverse biasing voltage if said stored signal identifies the second type of photodiode circuit by comparing a biasing voltage value at the second output with a reference biasing voltage value and accordingly to a result of this comparison applying a variable current to the first output.
Yet another solution to the above described problem is according to the present invention found in a method for controlling an intensity of a light source in which following steps are comprised:
connecting either one of a first or a second type of photodiode circuit to a detection circuit,
adapting said detection circuit for the first or the second type of the photodiode circuit connected to it,
receiving on at least a photodiode of the first or the second photodiode circuit light emitted by said light source,
obtaining at an output of the detection circuit a photovoltage of a predetermined polarity,
regulating an intensity of the light source such to maintain the photovoltage at a reference photovoltage value.
The method further comprises the steps of:
disconnecting the detection circuit from the first or the second type of photodiode circuit,
connecting to the first or the second type of photodiode circuit a test circuit,
determining at least whether the second type of photodiode circuit is connected to the test circuit,
storing a positive value if the determining reveals the second type of photodiode circuit,
disconnecting the test circuit,
performing the adapting for said second type of photodiode circuit if the stored result is positive, or else for the first type of photodiode circuit.
Yet another solution to the above described problem is according to the present invention found in an automatically adapting forward or reversed biased photodiode detection circuit comprising a first and a second input for connecting a photodiode circuit, the first input being connected to ground over a first switch, the second input being connected over a second switch to a current source and over a third switch to voltage evaluating means. The detection circuit further comprises first switching for simultaneously opening or closing the first, second and third switches, regulating means having an input connected over a fourth switch to the second input and an output connected over a fifth switch to the first input to regulate a biasing voltage at the second input to a predetermined reverse biasing voltage. Furthermore, it comprises second switching means for simultaneously opening or closing the fourth and fifth switches, these being connected to an output of said voltage evaluating means and to the first switching means.
The detection circuit according to the invention is a simple way of realizing the method for automatically obtaining a forward or a reversed biased photodiode device.
In a preferred embodiment of the detection circuit the voltage evaluating means comprise a voltage source which generates a predetermined reference voltage, a voltage comparator one input of which is connected to the voltage source, another input of which is connected to the third switch, a memory device to store a result of a comparison delivered at an output of the voltage comparator.
In another preferred embodiment of the detection circuit the regulating means comprise a further voltage source which generates the predetermined reversed biasing voltage, an amplifier an input of which is connected to the further voltage source, another input of which is connected to the fourth switch, an output of which is connected to the fifth switch.
Yet another solution to the above described problem is according to the invention found in a light intensity monitoring and controlling circuit which comprises an automatically adapting forward and reversed biased photodiode detection circuit as described above, further voltage evaluating means to determine a photovoltage value of a voltage between the first and second input, the further evaluating means having a first and a second evaluating input connected to the first and the second input through a sixth and a seventh switch respectively, the photovoltage value being emitted at an evaluating output, third switching means which allow to simultaneously open or close the sixth and the seventh switch and an input of which is connected to the second switching means, power regulating means which allow to regulate an intensity of a light source as a function of the photovoltage value, the power regulating means being connected to the evaluating output.
In a preferred embodiment of the light intensity monitoring and controlling circuit the power regulating means comprise a reference voltage source which generates a predetermined reference voltage, photovoltage comparing means to compare said predetermined reference photovoltage with the photovoltage, a result of the photovoltage comparing being used to regulate the intensity.
The light intensity monitoring and controlling circuit allows a simple realization of the method for controlling an intensity of a light source according to the invention.